1. Field of the Invention
This invention relates to long term evolution of WCDMA (Wideband Code Division Multiple Access). In particular, the invention is related to defining a frame structure to efficiently search parameters in a multi-band Orthogonal Frequency Division Multiplexing (OFDM) system during initial synchronization.
2. Description of the Related Art
Wireless communication systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users sequentially or simultaneously by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, and Orthogonal Frequency Division Multiple Access (OFDMA) systems, other types of multi-carrier access schemes, or any combinations of these.
Wireless communication systems divide areas of coverage into cells, each of which is served by a base station. A mobile station continuously monitors the signal strengths of a servicing base station for a current cell as well as for adjacent cells. The mobile station sends signal strength information to the network. As the mobile station moves toward the edge of the current cell, the servicing base station determines that the mobile terminal's signal strength is diminishing, while an adjacent base station will determine the signal strength is increasing. The two base stations coordinate with each other through the network, and when the signal strength of the adjacent base station surpasses that of the current base station, control of the communications is switched to the adjacent base station from the current base station. The switching of control from one base station to another is referred to as a handoff.
In the ever-continuing effort to increase data rates and capacity of wireless networks, communication technologies evolve. Multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems represent an encouraging solution for the next generation high-speed data downlink access. A benefit of such systems is their high spectral efficiency wherein all of the allocated spectrum can be used by all base stations. In OFDM modulation, the transmission band is divided into multiple, orthogonal carrier waves. Each carrier wave is modulated according to the digital data to be transmitted. Because OFDM divides the transmission band into multiple carriers, the bandwidth per carrier decreases and the modulation time per carrier increases. Since the multiple carriers are transmitted in parallel, the transmission rate for the digital data, or symbols, on any given carrier is lower than when a single carrier is used. During initial synchronization, various systems and implementations are used that require operation in a variety of possible bandwidths. Also, the number of parameters that has to be searched during initial synchronization is large, thus, the frame structure has to be defined.
A special Short System Information (SSI) message present in every frame provides information pertaining to the wireless communication system, which is receivable by all terminals. Thus, the SSI has to be received by the terminals with good probability in all propagation and mobility conditions, in any reasonable cell deployment, and with any of the specified system bandwidths. In addition to frame synchronization, system bandwidth in a scalable bandwidth system (as Evolved Universal Terrestrial Radio Access Network (E-UTRA)), and the operation bandwidth is determined by receiving the SSI during the initial synchronization. In handover, the system bandwidth is given in the neighbor list, and decoding of the SSI is actually necessary mainly for frame timing detection. There is, therefore, a need in the art for a pilot structure and method that enables faster and more reliable finding of the system information message during the initial synchronization and during handover (preparation) in all propagation, mobility and interference conditions. The mobility conditions may include a receiver velocity up to 350 km/h.
Accordingly, an apparatus and method are needed to provide a signal structure that may enable a MS (mobile station) to synchronize and read messages from a BS (base station) without knowledge of the specific bandwidth (bandwidth). Contrary to conventional systems, the apparatus and method would not require numerous tests of numerous parameter combinations.